Sulfur K-Edge XAS and DFT Calculations on Nitrile Hydratase: Geometric and Electronic Structure of the Non-heme Iron Active Site
| Autor: | Keith O. Hodgson, Maeda Mizuo, Kayoko Taniguchi, Marina S. Chow, Masafumi Odaka, Julie A. Kovacs, Steven D. Davin, Abhishek Dey, Britt Hedman, Priscilla Lugo-Mas, Edward I. Solomon |
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| Jazyk: | angličtina |
| Rok vydání: | 2006 |
| Předmět: |
Models
Molecular X-ray absorption spectroscopy Binding Sites biology Absorption spectroscopy Chemistry Stereochemistry Active site Spectrometry X-Ray Emission Protonation General Chemistry Antibonding molecular orbital Biochemistry Catalysis Molecular electronic transition Article Nonheme Iron Proteins Crystallography Colloid and Surface Chemistry Models Chemical Oxidation state Nitrile hydratase biology.protein Hydro-Lyases |
| Popis: | The geometric and electronic structure of the active site of the non-heme iron enzyme nitrile hydratase (NHase) is studied using sulfur K-edge XAS and DFT calculations. Using thiolate (RS(-))-, sulfenate (RSO(-))-, and sulfinate (RSO(2)(-))-ligated model complexes to provide benchmark spectral parameters, the results show that the S K-edge XAS is sensitive to the oxidation state of S-containing ligands and that the spectrum of the RSO(-) species changes upon protonation as the S-O bond is elongated (by approximately 0.1 A). These signature features are used to identify the three cysteine residues coordinated to the low-spin Fe(III) in the active site of NHase as CysS(-), CysSOH, and CysSO(2)(-) both in the NO-bound inactive form and in the photolyzed active form. These results are correlated to geometry-optimized DFT calculations. The pre-edge region of the X-ray absorption spectrum is sensitive to the Z(eff) of the Fe and reveals that the Fe in [FeNO](6) NHase species has a Z(eff) very similar to that of its photolyzed Fe(III) counterpart. DFT calculations reveal that this results from the strong pi back-bonding into the pi antibonding orbital of NO, which shifts significant charge from the formally t(2)(6) low-spin metal to the coordinated NO. |
| Databáze: | OpenAIRE |
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